Electronic systems employing analog circuitry along with microprocessors, DSPs, ASICs, and FPGAs has many different power supply rails. The on-off timing, rise and fall rate, order of application, and magnitude of each of the supply voltages needs to be controlled for reliable, repeatable operation. Power system design includes supply sequencing, supply tracking, supply voltage/current monitoring and control. A variety of power management ICs exists to perform the functions of sequencing, tracking, and monitoring for both power-up and power-down.
Power supply tracking is based on the fact that power supplies cannot provide instantaneous changes in their voltage; this can be used advantageously by power system designers in controlling the slew rate of each of the various supplies in relation to other supplies in the system.
Power supply tracking systems handle a variety of power-up profiles to satisfy the requirements of digital logic circuits including FPGAs, PLDs, DSPs and microprocessors. Some applications require that the potential difference between two power supplies must never exceed a specified voltage. This requirement applies during power-up and power-down as well as during steady-state operation, often to prevent destructive latch-up in a dual supply ASIC. Typically, this result is achieved by ramping the supplies up and down together. In other applications it is desirable to have the supplies ramp up and down with fixed voltage offsets between them or to have them ramp up and down ratiometrically.
During turn-on of dual voltage ICs, circuits powered by Input/Output (IO) voltage can be in state that draws excessive current because core voltage is below minimum voltage to ensure logic is in proper state. This condition may create a problem in some circumstances when supplies did not have the capability to provide this large current, and consequently would not become operational. Typically boards are provided which have limited available voltages (lower voltages must be generated on-card), which limits options on controlling sequencing.
Heretofore it has been necessary to provide oversized power systems, or to add complex circuitry which requires the availability of board space and proper voltages for biasing.
A need, therefore exists for an improved way to deal with a high inrush current when voltage is applied to mixed voltage logic.